An Incubus (インキュバス) is a member of the Incubi, also called Inmazoku (淫魔族, lewdness demon tribe). The Incubus is one of the ancient extinct races of Álfheimr. They are the male version of the Succubi. According to Ini, it's theorized that the Incubus and Succubus were the male and female counterparts of the same race at some point.
Like Succubi, Incubi show an all-encompassing love for men and women of all ages and are a race that mates with all other races with their nondiscriminatory love. Ini hypothesizes that, like the Nótt Álfur in Álfheimr, Incubi might have crossed over to other worlds, leaving behind descendants in said worlds. She hints that Naoya could actually be an Incubus descendant.
As the story progresses, Ini's hypothesis is proved correct when Naoya uses the Dvergur Miraculous Spring when he visited Holti's Kindgom. Originally, Naoya appears to collapse due to alcohol when, in fact, it is later shown that he has a very high alcohol tolerance (far above all people in Rotte's manor). The spring's effects caused his latent Incubus blood to awake to the point of eventually falling pray to the Incubus' Dream Bondage, an Incubus-exclusive condition that can only be cured by a Succubus.
Within the story, while not pure, Naoya is the only Incubus and Asuha, his and Mercelída's daughter, has the blood of both an Incubus and a Succubus, making her a Succubus with all the abilities but none of the weaknesses.